1. Field of the Invention
The present invention relates to an AC-DC (alternate current-direct current) converter for converting alternating current to direct current. More particularly, the invention relates to a technique of reducing an input current in outputting a peak voltage.
2. Description of the Related Art
FIG. 1 shows a constitution of a conventional AC-DC converter disclosed in U.S. Pat. No. 5,960,207. The AC-DC converter includes a rectifier DB consisting of a diode bridge, an active power factor controller (PFC) 11, an input capacitor Cin and a DC-DC (direct current-direct current) converter (D/D) 12. The AC-DC converter operates as follows.
In operation, the rectifier DB rectifies AC power (85˜265V) supplied from a commercial power source AC and outputs the full-wave rectified power to the power factor controller 11. If the power factor controller 11 is a type of global use, it boosts an output voltage of the rectifier DB to D.C. 380V. As a result, a voltage Vc on an input capacitor Cin of the DC-DC converter 12 connected to output terminals of the power factor controller 11 becomes D.C. 380V. Meanwhile, the power factor controller 11 allows the waveform of an input current to follow the waveform of an input voltage to improve a power factor of the AC-DC converter.
The DC-DC converter 12 inputs a D.C. voltage Vc supplied from the power factor controller 11 through the input capacitor Cin and further converts the voltage Vc to another D.C. voltage. The so-converted D.C. voltage (as an output voltage Vo) is supplied from output terminals +Tout, −Tout of the DC-DC converter 12 to a not-shown load.